The broach, being a broaching instrument, is comprised of a sequence of separate cutting blades known as cutting teeth that span its whole length. Feed is achieved by the greater distance between each pair of adjacent teeth on the broach. The cumulative amount of material removed in a single pair of the broach is determined by the combined action of all the teeth in the tool. It is not required for all the teeth in the broach to be in operation simultaneously. The cutting speed of the broach is determined by the tool’s linear motion relative to the workpiece.
The contour of the cutting edges on the broach determines the shape of the cut surface, also known as the machined surface. Broaches are often constructed from high speed steel (HSS). Occasionally, the broaches are constructed from cast iron and their cutting blades are composed of cemented carbide inserts. These inserts are securely affixed to the correct location either by mechanical methods or by brazing.
Terminology for a Pull Type of Broaching Tool
The specification of a broach refers to the nomenclature of the broach as stated using numerical numbers. The following text provides an explanation for this terminology.
Pull End
The pull end is designed to connect the broach to the broaching machine using the puller head.
Front Pilot Broaching
This aligns the broach precisely in the hole that has to be completed, right before the procedure begins.
Roughing Teeth
These cutting blades are designed to efficiently remove a significant amount of material during the cutting process. Increasing the amount of material removed results in a worse quality surface finish, but it also speeds up the procedure.
Polishing Teeth
These cutting blades are used to remove tiny amounts of material. These tools are utilized for the precise size and final polishing of surfaces.
Rear Pilot and Follower Rest
This is an auxiliary device used in conjunction with a broach to facilitate the completion of the broaching process.
Land
The flank face width of the broach refers to the measurement of its breadth. Typically, it is somewhat inclined to provide a relief angle to the flank face of the broach.
Pitch
Pitch refers to the measurement of the distance between two matching places on consecutive teeth of a broach. Typically, the pitch of the finishing teeth on a broach is less than that of the rough cutting teeth.
Dental height
The height of the roughing and finishing teeth progressively increases from the shank to the finishing teeth. The increment in question is referred to as the cut per tooth, and its value is contingent upon the material being subjected to machining. Typically, the amount of material removed per tooth ranges from 0.01 to 0.2 mm for the finishing teeth, and it can up to 0.2 mm for the cutting teeth.
Terminology for an External Broaching Tool
External or surface broaching is a machining process that eliminates material from the outside layer of the workpiece. Similar to pull-through and push-through broaches, the teeth of surface broaches gradually grow in size.
- Land: Land refers to the area located at the base of the teeth and serves as a foundation for the cutting edge.
- Rake: Rake refers to the angle at which the cutting tool comes into contact with the workpiece. As the cutting tool cuts the workpiece, the chips that are produced during the cutting process travel along the rake.
- Pitch: Pitch refers to the measurement of the distance between the cutting edges of two teeth.
- Clearance Angle: The clearance angle refers to the inclination of the land with respect to the horizontal axis, specifically intended to minimize friction between the teeth and the workpiece. It guarantees that only the most advanced part of the teeth come into touch with the workpiece.
- Depth: Depth refers to the vertical measurement of each tooth, specifically its height.
- Gullet Radius: The gullet radius refers to the radial gap between two adjacent teeth, which serves as a pathway for the chips to flow through once they have been curled.
- Chipbreaker: A chipbreaker is a device used in machining to break up chips and improve the efficiency of the cutting process.
Chipbreakers are indentations employed to prevent the accumulation of chips and aid in their removal. The roughing and semi-finishing teeth are ground parallel to the tool axis. Chipbreakers are arranged in a staggered pattern, with a series of chipbreakers followed by cutting teeth. They play a crucial role in round broaching tools by preventing the formation of ring-shaped chips. - Side Relief: During the process of broaching slots, the tool becomes surrounded by the slot during cutting and transports the chips along the whole length of the tool. The teeth of the broach come into contact with the sidewalls of the slot and experience abrasion. A singular relief angle on the lateral surfaces of the teeth minimizes friction and abrasion, while preserving a short section adjacent to the sharp cutting edge.
Different Types Of Broaches
Broaches or broaching tools come in various shapes and types, each designed for specific applications and cutting requirements. Below are some common broaching tool shapes and types although custom broaches are widely used in the manufacturing industry.
Keyway Broaches
Almost all keyways in machine tools and parts are cut using a keyway broach, which is a small, flat bar with cutting teeth spaced along one surface. These broaches are capable of cutting both internal and exterior keyways. Internal keyways often require a slotted bushing or horn to fit the hole, with the keyway broach being pushed through the horn and guided by its slot.
- This broaching tool is used to cut keyways, which are slots that hold keys or other mating components.
- Available in a variety of sizes to accommodate varied keyhole diameters.
Square Broaches
- Designed to cut square holes or forms.
- Often used in applications that demand a perfect square form.
Hexagonal Broaches
- Used to carve hexagonal holes or forms.
- Bolts, nuts, and other hexagonal-shaped components are frequently manufactured using this material.
Round Broaches
The simplest sort of broach is a circular one. This is a circular bar that creates holes similar to those generated by a drill press. The distinction is that a broach cut is faster, cleaner, and allows for tighter tolerances. Round broaches may be used to quickly create precise holes and are ideal for high-volume mass manufacturing.
Splined Broaches
Spline broaches allow operators to cut a series of teeth or notches around the perimeter of a previously cut hole. This specific design is extremely important in the automobile sector, as splines are used extensively in driveshafts, gearboxes, and other components. The ridges along the spline’s perimeter provide an effective way of transmitting power from one area to another, as the component that fits within will have no wiggle space. Broaching guarantees that the high-tech components’ precision requirements are met.
- Used to cut splines, which are longitudinal ridges or teeth on a shaft.
- Important in the manufacture of gears and other components with spline connections.
Dovetail Broaches
- A cutting tool used to create dovetail-shaped grooves or slots.
- Commonly utilized in applications that need a sliding or locking mechanism.
Internal Broaches
- Finishing teeth are meant to cut interior details on a workpiece.
- Depending on the individual demand, it may be square, hexagonal, spherical, or other forms.
External Broaches
- Used to cut the exterior surfaces of a workpiece.
- Can generate exterior forms like flats, hexagons, and other geometries.
Surface Broaches
The slab broach is the most basic surface broach. It is a general-purpose instrument that cuts flat surfaces.
- Finishing teeth are meant to cut flat surfaces of a workpiece.
- Used to achieve a smooth and uniform surface finish.
Involute Gear Broaches
- Specifically developed to cut involute gears.
- Gear manufacture requires accurate tooth profiles to provide smooth gear engagement.
Serrated Broaches
- Used to cut serrations, which are a series of notches or teeth.
- Serrated surfaces are commonly used in applications that need grasping or locking.
Taper Broaches
- Finishing teeth are meant to create tapered holes or forms.
- Useful in applications that need a progressive decrease in diameter.
Oval Broaches
- Used to cut oval or elliptical forms.
- Used in instances where a non-circular aperture is required.
These are only a few examples, and the variety of broach forms reflects the wide range of applications and machining requirements across industries. The preferred broach type is determined by parameters such as the desired feature, workpiece material, and unique production constraints.
How Broaches Work
The broach is often a slender rod that is inserted into the workpiece, causing the hole to adopt the form of the rod’s outer surface. There are no sparks, no little pieces of metal flying, and no difficult, lengthy incisions needed. Frequently, initiating a conversation or topic just requires a few seconds rather than several minutes.
The efficiency of this procedure is determined by the design of the broach itself. A common variety of linear broach employs a metallic rod to create a certain shape in the workpiece. The bar is equipped with teeth designed to extract metal from the item. Each tooth of the broach is successively bigger than the previous one, resulting in the removal of somewhat more material from the workpiece as the broach moves through it. The ultimate tooth is precisely molded to match the intended cut.
The initial teeth of a broach are specifically engineered to perform a coarse cut, eliminating a greater amount of material compared to the subsequent teeth. The subsequent set of teeth subsequently execute more accurate incisions, carrying out a semi-finalizing task. The last set of teeth produces the most precise incisions, resulting in a smooth and precise outcome. In addition, the broach has effectively removed all the metal shavings off the object, minimizing the need for cleaning.
Broaches may have a somewhat greater initial expense compared to other components of similar size in the field of machining. However, they can exhibit remarkably extended lifespans if properly sharpened. Colonial Tool provides sharpening services that significantly extend the lifespan of your broach.
How To Care For Your Broaches?
When you obtain a new broach, it is probably excellent for at least 8,000 cuts. However, if the broach is well-maintained and sharpened on a regular basis, the initial estimate might be increased to approximately 60,000 or more cuts.
Broaches are expensive items, with some costing $2,000 or more, and although the predicted 8,000 cuts may be sufficient for smaller operations, not every business can afford to replace these tools so regularly.
As a result, after cutting 3,000 components, it may be worthwhile to send your broaches out to be sharpened and reconditioned in order to extend their useful life and lower total production costs. If you observe an increase in the force required to cut your components, your broach may need to be sharpened.
Conclusion
Broaches are one of the most versatile, powerful tools available to machine shops, hobbyists and manufacturers today. If you’re looking for the right broach tool to suit your needs, browse our selection of broaching tools and contact us to learn more about those that interest you. We pride ourselves on offering the highest-quality broaches available anywhere.